\loop, tabular ignores new row

Question

I'm trying to get this "timeline" thing going for a document I'm writing. Follows the code I've got so far:

\documentclass{article}
\usepackage{etoolbox}
\newcommand{\addTimeline}[3][]{%
\ifcsname timeLine#2\endcsname
  \expandafter\appto\csname timeLine#2\endcsname{ #3 #1\\}
\else
  \expandafter\csdef{timeLine#2}{{\bf #2}  #3  #1\\}
\fi
}

\newcommand{\gentimeLine}[2]{
\newcount\tmpc
\def\tabledata{}
\tmpc=#1
\loop \ifnum \tmpc<#2 
   \expandafter\csuse{timeLine\the\tmpc}
   \advance \tmpc 1
\repeat 
}

\begin{document}

\addTimeline{10}{Test1}
\addTimeline{20}{Test2}
\addTimeline{13}{Test3}
\addTimeline{25}{Test4}

\def\tabData{\gentimeLine{1}{26}}
\tabData

-

\begin{tabular}{c}\hline   
  \tabData
\end{tabular}

\end{document}

Naturally, in \addTimeline command I intend to have #2 & #3 & #1 and {c c c} in tabular instead, but for testing purposes I am keeping it in one column one.

The expected output was

10 Test1
13 Test3
20 Test2
25 Test4

followed by the table with those entries, each in a respective row.

But instead I get a table with only one row, containing the first entry 10 Test1. The 4 items are correctly printed in normal text, however.

Any suggestions on how to fix?

Answer 1

You can't start the loop in one table cell and end it in another one. Thus I use \tabledata as a container that's filled and then delivers the table body all at once.

\documentclass{article}
\usepackage{etoolbox}

\newcommand{\addTimeline}[3][]{%
  \csappto{timeLine#2}{\unexpanded{\textbf{#2}  #3  #1\\}}%
}

\newcount\tmpc
\newcommand{\gentimeLine}[2]{%
  \def\tabledata{}%
  \tmpc=#1\relax
  \loop \ifnum \tmpc<#2
    \edef\tabledata{\expandonce{\tabledata}\csuse{timeLine\the\tmpc}}%
    \advance \tmpc 1
  \repeat
  \tabledata
}

\begin{document}

\addTimeline{10}{Test1}
\addTimeline{20}{Test2}
\addTimeline{13}{Test3}
\addTimeline{25}{Test4}

\def\tabData{\gentimeLine{1}{26}}

\begin{tabular}{c}\hline
  \tabData
\end{tabular}

\end{document}

Notes

1. etoolbox already offers \csappto that will create the macro if not existing

2. \newcount must go outside the macro using the counter, or it will create a new one at each call

3. the \unexpanded in the definition of \addTimeline might be bad for other uses of timeLine<number>

Here's the output:

An implementation in expl3:

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\NewDocumentCommand{\addTimeline}{omm}
 {
  \tl_clear_new:c { l_benedict_timeline_#2_tl }
  \tl_put_right:cn { l_benedict_timeline_#2_tl } { \textbf{#2}~#3 }
  \IfValueT{#1}
   {
    \tl_put_right:cn { l_benedict_timeline_#2_tl } { ~#1 }
   }
  \tl_put_right:cn { l_benedict_timeline_#2_tl } { \\ }
 }

\NewDocumentCommand{\genTimeline}{mm}
 {
  \tl_clear:N \l__benedict_timeline_body_tl
  \int_step_inline:nnnn { #1 } { 1 } { #2 }
   {
    \tl_if_exist:cT { l_benedict_timeline_##1_tl }
     {
      \tl_put_right:Nv \l__benedict_timeline_body_tl { l_benedict_timeline_##1_tl }
     }
   }
  \tl_use:N \l__benedict_timeline_body_tl
 }

\tl_new:N \l__benedict_timeline_body_tl
\cs_generate_variant:Nn \tl_put_right:Nn { Nv }
\ExplSyntaxOff

\begin{document}

\addTimeline{10}{Test1}
\addTimeline{20}{Test2}
\addTimeline[again]{20}{Test2}
\addTimeline{13}{Test3}
\addTimeline{25}{Test4}

\begin{tabular}{c}
\hline
\genTimeline{1}{26}
\hline
\end{tabular}

\end{document}